fix Issue 2481 - mixing field into anonymous struct inside class generates field overlapping vtable
fix Issue 3991 - Void initializers in unions considered overlapping
fix Issue 6439 - [CTFE] union fields are initialized independently
fix Issue 8511 - Segfault with forward-referenced enum
fix Issue 8255 - [CTFE] ICE when passing 'ref' literal
Merge pull request #2778 from 9rnsr/worksforme

[trivial] Add test cases for WORKSFORME issues